Week #6: Overnight Water? EWWW

Have you ever drunk a cup of water you forgot and left outside overnight? Do you recall the taste of it? I've experienced this before, and trust me it was like vomiting taste that I developed a habit of putting my water back in the fridge every night before bed. Why does this happen?

INTRODUCTORY VIDEO

  

Standard YouTube license: Why Does Water Go Stale Overnight? uploaded by SciShow

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DISCUSSION 

Some common substances found in our drinking water besides H₂O (obviously) are¹:

• Minerals: mostly Ca²⁺ and Mg²⁺
• Sulfates (SO₄^2-): resulted by natural deposition of magnesium sulfate (MgSO₄), calcium sulfate (CaSO₄), or sodium sulfate (Na₂SO₄). These can be removed, and the maximum concentration allowed is 250mg/L*. 
• Iron (Fe): resulted by natural deposition or through the use of iron pipes in water distribution system. The maximum concentration is 1.0mg/L*. 
• Chlorides (Cl^-): mostly existed due to pollution from sea water and industrial wastes. The acceptable concentration is below 250mg/L*. 

When water absorbs carbon dioxide gas, they react to produce carbonic acid based on the below reaction:

H₂O(aq) + CO₂(g) --> H₂CO₃(aq)  

This reaction may look familiar because it also explains how acid rain happens as rain falls down to Earth and absorbs CO₂ released from pollution in the air².

Other substances from pollution which lead to acid rain

Chlorination is to purify water, so the primary purpose of using chlorines is to disinfect water and kill germs. The method was first used in the U.S. in 1908 and a level of 4mg/L* is safe for drinking³. Chlorination affects water's taste, and some people may not like it. As stated in the video, cold water often tastes better, so if you don't like the taste of your water, toss it in the fridge for a while and drink it hours later. I'm too often disgusted by the taste of my water here in the States, so my personal solution is to drink it with fruit flavor powder (such as those from Crystal Light - my favorite flavor is Cherry Pomegranate). These powder packs do not contain sugar, with a very small amount of calories. It can be a substitute for soft drinks if you want to drink something sweet but healthier.

A simple sketch of chlorination process

Finally, you may want to still drink your overnight water since there isn't any health concerns related. However, for picky people like me who are pretty sensitive to taste, just put your water in the fridge before you go to bed :)

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* In some articles, the unit used may be ppm (parts per million), which simply means mg/L.
Sources
Thumbnail background from CDXLIFE
Acid rain image from Nualgi Ponds
Chlorination process image from Pure Water Products LLC
¹ Commonly Found Substances in Drinking Water and Available Treatment from Illinois Department of Public Health
² Free Carbon Dioxide in Water
³ Drinking Water Quality Regulator for Scotland